From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030909Ab2CFPbl (ORCPT ); Tue, 6 Mar 2012 10:31:41 -0500 Received: from casper.infradead.org ([85.118.1.10]:44115 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030447Ab2CFPbj convert rfc822-to-8bit (ORCPT ); Tue, 6 Mar 2012 10:31:39 -0500 Message-ID: <1331047870.11248.314.camel@twins> Subject: Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine call_srcu() From: Peter Zijlstra To: Lai Jiangshan Cc: Lai Jiangshan , "Paul E. McKenney" , linux-kernel@vger.kernel.org, mingo@elte.hu, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, patches@linaro.org Date: Tue, 06 Mar 2012 16:31:10 +0100 In-Reply-To: References: <1331023359-6987-1-git-send-email-laijs@cn.fujitsu.com> <1331027858-7648-1-git-send-email-laijs@cn.fujitsu.com> <1331027858-7648-5-git-send-email-laijs@cn.fujitsu.com> <1331034734.11248.287.camel@twins> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2012-03-06 at 22:44 +0800, Lai Jiangshan wrote: > >> + if ((++idle_loop & 0xF) == 0) { > >> + spin_unlock_irq(&sp->gp_lock); > >> + udelay(1); > >> + spin_lock_irq(&sp->gp_lock); > >> + } > > > > The purpose of this bit isn't quite clear to me, is this simply a lock > > break? > > Yes, the main purpose is: > make the time of sp->gp_lock short, can be determined. either introduce cond_resched_lock_irq() or write something like: if (need_resched() || spin_needbreak(&sp->gp_lock)) { spin_unlock_irq(&sp->gp_lock); cond_resched(); spin_lock_irq(&sp->gp_lock); } udelay(1) is complete nonsense..